Photochromic element

ABSTRACT

A PHOTOCHROMIC ELEMENT IN THE FORM OF A BASE SHEET HAVING A COATING CONTAINING AN INORGANIC PHOTOCHROMIC COMPOUND IN THE FORM OF A TUNGSTIC OR MOLYBDIC ACID AND THEIR COMPLEXES WITH PHOSPHORIC ACID AND A PHENYLGLYCOLIC ACID AND DERIVATIVE WHICH ENHANCES THE DEPTH OF COLOR DEVELOPED IN RESPONSE TO EXPOSURE TO ULTRA-VIOLET LIGHT.

United States Patent 3,687,672 PHOTOCHROMIC ELEMENT Alexander Averbach, Skokie, Ill., assignor to A. B. Dick Company, Niles, Ill. No Drawing. Filed Nov. 1, 1968, Ser. No. 772,799 Int. Cl. G03c 1/52 U.S. Cl. 9690 PC 4 Claims ABSTRACT OF THE DISCLOSURE A photochromic element in the form of a base sheet having a coating containing an inorganic photochromic compound in the form of a tungstic or molybdic acid and their complexes with phosphoric acid and a phenylglycolic acid and derivative which enhances the depth of color developed in response to exposure to ultra-violet light.

This invention relates to a photographic process for producing images by the use of photosensitive, inorganic, photochromic or phototropic substances which experience a color change upon exposure to light.

Photochromic compounds may be subdivided into the organic substances represented by spyrans and inorganic substances represented by heteropoly acids of tungsten or molybdenum. This invention has to do with the latter group of inorganic photochromic materials and their utilization in the production of images by reason of their longer reversion period, as is or in stabilized form, whereby they are better adapted for printout and other copy processes. The sensitivity of such inorganic heteropoly acids of tungsten and molybdenum has been found greatly to be increased when employed in the form of tungstic or molybdic complexes with phosphoric, boric or silicic acids, including mixtures of such tungstic or molybdic complexes.

Photochromic compounds and complexes thereof and their use in photosensitive products are well known in the art and, for such purposes, reference may be made to the following United States patents: No. 1,934,451; No. 2,427,443; No. 2,895,892; No. 2,981,622; No. 3,169,064; No. 3,236,651; No. 3,285,746; No. 3,293,037 and No. 3,322,552.

Such photochromic processes and compositions have not found widespread use in the copy field because of the inability to obtain sufficiently deep colors or hues for color contrast of the type desired in good copy quality. For the most part shades of grey are produced as distinguished from a desirable deep black for color contrast.

Furthermore, systems of the type heretofore produced are characterized by too rapid reversion following removal of the ultra-violet light whereby the image remains for only a relatively short period of time.

It is an object of this invention to provide a photochromic system of the type described which is capable of use to provide sensitive coatings which are capable of developing color of high intensity and deep shades in response to exposure, as to ultra-violet light; which retain the developed color over relatively long periods of time without reversion to the original photochromic layer; which provides layers of high sensitivity for the development of images of good quality in a simple and efiicient manner; and which is capable of application to produce photosensitive sheets or film for print-out and the like.

As described in the aforementioned patents, such tungstic and molybdic acids and their complexes with acids, such as phospho-tungstic acid, are used with carbonaceous reducing agents to effect color development upon exposure to light. Thus it was wholly unexpected to find that deep, bluish-black images can be obtained 3,687,672 Patented Aug. 29, 1972 when such tungstic and molybdic heteropoly acids are reduced under ultra-violet light in the presence of mandelic acid (phenylglycolic acid) or alpha-hydroxy alpha-toluic acid derivatives thereof, as represented by the formulae:

I. H o o0om II. HXC-COOILRz R R] R/ R1 in which X is 0 or S, R is an aryl or a substituted aryl group, R is hydrogen, alkyl, alkoxy, alicyclic, aryl or substituted aryl group, R is hydrogen or an alkyl, aromatic, alicyclic, arylalkyl, substituted aryl or substituted arylalkyl group in which the alkyl groups identified above may be represented by methyl, ethyl, propyl, butyl to octadecyl, the alkoxy group may be represented by methoxy, ethoxy, propoxy, butoxy, etc., the aryl group may be represented by benzyl, naphthyl, anthracyl and the like the arylalkyl group may be represented by phenyl, toluyl and the like, and the substituted groups may be represented by halogen, amino, hydroxy, carboxyl and the like groups. Representative of such of the foregoing would include 4-butyl phenyl, 3,4-hydroxy phenyl, 4- chloro phenyl, 4-isopropy1 phenyl, 4-methoxy phenyl, cyclohexyl and the like. R is a compound capable of forming an adduct compound such as methenamine and benzylamine. Representative are such compounds as mandelic acids (R=phenyl; R and R =hydrogen; X=oxygen); benzilic acids (R and R =phenyl; R =hydrogen; X=oxygen); methyl mandelate (R-=phenyl; R =hydrogen; R =CH X=oxygen), adduct of mandelic acid and methenamine, adduct of mandelic acid and benzylamine.

Tungstic and molybdic heteropoly acids which may be used in the practice of this invention are represented by silico-lZ-tungstic acid, H Si W O boro-lZ-tungstic acid, H BW O phospho-lZ-tungstic acid, H PW O phospho-9-tungstic acid, H P'W O phospho 12 molybdic acid, H PM0 O silico-l2-molybdic acid, H SiMo O phospho-l2-tungstomolybdic acids. The heteropoly acids may be used singly or in admixture with each other. The term heteropolyacid is here used generically and includes both free acids and their salts in which one or more of the hydrogen ions shown in the formulae above have been replaced by another cation, usually an alkali metal ion. These salts are themselves acid in solution.

Reducing agents which have been employed with such photochromic compounds are of the carbonaceous type described more fully in U.S. Pat. No. 2,981,622. Such reducing agents may be employed in the practice of this invention in addition to but not instead of the mandelic acid and derivatives, as described herein.

As binders for the coating, use can be made of various film formers such as polyvinyl butyral, polyvinyl acetate, polyvinyl pyrrolidone, polyacrylamide, gelatin, vegetable gum, polyvinyl alcohol resins and pliolite with water soluble film forming materials being preferred.

Having described the basic concepts of this invention, illustration will now be made with reference to the following examples:

EXAMPLE 1 Percent by weight Phosphotungstic acid 14 Mandelic acid 7 7 Polyvinyl alcohol (Elvanol 72-51) 9.5 Distilled water 69.5

photographic fidelity in that an image of high contrasting color was produced. The speed of the paper was about twice that of conventional oxalid paper.

By comparison with the same sheet coated with the same composition in the same amounts, but in the absence of mandelic acid, the copy produced was rather weak.

The copy produced in a sheet prepared in accordance with the practice of this invention faded very slowly over a long period of time, when kept in the dark.

The concentration of ingredients in the coating composition can be varied over a fairly wide range without material effect on the copy and with little, if any, variation in copy quality. Little variation in copy quality results from variation in the thickness of the coating. It is preferred, however, to make use of the phenylglycolic acid component in the coating composition in an amount within the range of 1 part by weight of the phenylglycolic acid component or mandelic acid component to 1 to 10 parts by weight of phosphotungstic or phosphomolybdic acid.

For further examples of coating composition formulated of the components including film former, phosphotungstic or phosphomolybdic acids and reducing agents, reference may be had to the aforesaid patents, which are incorporated herein by reference, but with the modification to add mandelic or the like phenylglycolic acid component in the ratio of 1 part by weight per 1 to 10 parts by weight of the photochromic component.

The following are further examples of the practice of this invention:

EXAMPLE 2 Parts by weight Phosphotungstic acid 2-10 Solution polyvinyl butyral 5-50 Isopropylalcohol (90 parts) 510 Ethyl alcohol 210 Mandelic acid derivative .5-5

In the foregoing example, the mandelic acid derivative may constitute one or more of the compounds previously identified in the specification and the butyral solution may be substituted with others of the film forming materials previously identified.

It will be apparent from the foregoing that I have provided a new and improved photochromic coating which is capable of better color intensity for improved copy quality with greater premanence in the copy that is formed.

It will be understood that changes may be made in the details of formulation and operation without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. A photochromic element comprising a base sheet and a coating on the surface of the base sheet containing an inorganic photochromic compound selected from the group consisting of heteropoly tungstic and molybdic acids and their acid complexes, a binder and a phenylglycolic acid or derivative thereof in the ratio of 1 part by weight per 1 to 10 parts by weight of the photochromic component represented by the formulae:

in which X is oxygen or sulphur, R is an aryl or substituted aryl group, R is hydrogen, aryl or substituted aryl group, R is hydrogen, alkyl, aryl, arylalkyl, substituted aryl or substituted arylalkyl group, and R is a compound capable of forming an adduct.

2. A photochromic element as claimed in claim 1 in which the phenylglycolic acid or derivative is selected from the group consisting of mandelic acid, benzilic acid, methyl mandelate, an adduct of mandelic acid and methenamine, and an adduct of mandelic acid and benzylamine.

3. A photochromic element as claimed in claim 1 in which the inorganic photochromic compound is selected from the group consisting of a phosphotungstic and phosphomolybdic acid.

4. A photochromic element as claimed in claim 1 in which the adduct compound is selected from the group consisting of methenamine and benzylarnine.

References Cited UNITED STATES PATENTS 1,934,451 11/1933 Sheppard et a1. 9688 2,427,443 9/ 1947 Cochran 9688 2,895,892 7/1959 Chalkley 204-157.1 2,915,392 12/1959 Pedersen 9648 X 2,981,622 4/ 1961 Chalkley 9648 3,169,064 2/1965 Levy 117-34 X 3,236,651 2/1966 Marks et a1. 9688 3,285,746 11/1966 Marks et al. 350- X 3,293,037 12/1966 Chopoorian 9692 X 3,322,542 5/1967 Ullman et al 9690 3,322,552 5/1967 Roberts et al. 23-50 X WILLIAM D. MARTIN, Primary Examiner B. D. PIANALTO, Assistant Examiner US. Cl. X.R. 252-300 

